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Chapter 2 Astronomical Data WHO RUNS THE WORLD: DATA CHAPTER 2 ASTRONOMICAL DATA Hulusi GÜLSEÇEN*, Hasan H. ESENOĞLU** *Asos. Prof., İstanbul University, Science Faculty, Astronomy and Spaces Sciences Department, İstanbul, Turkey E-mail: [email protected] **Asos. Prof., İstanbul University, Science Faculty, Astronomy and Space Sciences Department, İstanbul, Turkey E-mail: [email protected] DOI: 10.26650/B/ET06.2020.011.02 Abstract Space telescopes have increased the quality of data collection for today’s astronomy. In parallel to this, obtaining high quality data with high technology and good resolution focal plane detectors in accordance with the developments in material science in the ground-based observations has been achieved. With the new generation of ground based and space observations, global campaigns also brought continuity in data acquisition and increased performance. Finally, the fact that theoretical outputs can be made to allow in today’s technology, for example, the detection of gravitational waves in the universe and these add new ones to the existing data. In addition, there has been a significant increase in data archiving, reduction and processing together with the number and variety of data collection tools. Astronomers have been able to overcome the facilitation in these processes in their own way: manpower waste has been reduced with autonomous telescopes, the data has been transformed into informatics (astroinformatics) with pipelines, the workload has been reduced to large masses by establishing a virtual observatory, and finally smart applications have been opened with the provided big data and new open areas have been reached with a future such as data mining. In this way, there has been progress in solving many astronomical events in the universe. This chapter is orginized in two subsections. In first, we are discussing how to solve problems in astronomy by using big data. In the second, we mention about big data sources in astronomy. The importance of data in astronomy, sources of data, big data in regards to the discovery of universe and analyzing data are the topics discussed in these subsections. Keywords: Astroinformatics, Astrostatistic, Astronomy, Big data, Machine learning, Processing, Reduction 14 ASTRONOMICAL DATA 1. Introduction Astronomy is the study of physics, chemistry, and evolution of celestial objects and phenomena that originate outside the Earth’s atmosphere, including supernova explosions, gamma ray bursts, and cosmic microwave background radiation (Zhang and Zhao, 2015). Since astronomy is a science that studies celestial bodies, the objects in space can only be investigated by examining the light coming or reflected from them. Thus, the only source astronomers have is light. There are many difficulties when investigating a celestial body. The Earth, the Sun and the Solar system are constantly in motion. Also, more distant celestial bodies such as stars and galaxies are constantly in motion. For this reason, the location of a celestial body at the time of observation, the position of the earth and the time of observation are very important. Studies with celestial bodies must be reduced to a heliocentric coordinate system. Observation time (which is one of the main parameters of astronomical data sets) should also be reduced to HJD (Heliocentric Julian Day). The time and the coordinates of both the celestial body and the detector (telescope, satellite, CCD, etc.) are indispensable parameters of a data set regardless of the wavelength in which the field of astronomy is studied. We can roughly divide astronomy into three areas of study. These are astrometric, photometric and spectroscopic studies. Roughly, we can classify the celestial objects to be observed as the sun, the objects of solar system, stars, Milky Way, galaxies, and galaxy groups. These celestial bodies are observed with different devices at different wavelengths of the electromagnetic spectrum. The classes of astronomy in terms of wavelength can be made as follows: gamma-rays astronomy, x-rays astronomy, ultraviolet astronomy, optical astronomy, infrared astronomy and radio astronomy. Astrophysics is the branch of astronomy that studies the physics of the universe, in particular, the nature of celestial objects rather than their positions or motions in space. Astrophysics typically uses many disciplines from physics, including mechanics, electromagnetism, statical mechanics, thermodynamics, quantum mechanics, relativity, nuclear, particle physics, and atomotic and molecular physics to solve astronomical issues (Zhang and Zhao, 2015). The occurrence times and life span of the events taking place in space also vary greatly. For example, gamma-ray bursts last for a few seconds while solar eruptions and binary star Hulusi GÜLSEÇEN, Hasan H. ESENOĞLU 15 eclipses last for a few minutes and several hours to years, respectively. The lives of stars last from ten million years to several billion years. Gamma-ray bursts (GRBs) in Astronomy are flashes of gamma-rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the brightest electromagnetic events known to occur in the universe after the big bang. Bursts can last from milliseconds to several minutes. The initial burst is usually followed by a longer-lived afterglow emitted at longer wavelengths (x-ray, ultraviolet, optical, infrared, microwave and radio). Targets of Opportunity (ToO) are astronomical objects undergoing unexpected/unpredictable transient phenomena and proposed for observation. The observations are normally urgent because of the transient nature of the event and may require even an immediate intervention at the telescope. ToO include objects that can be identified before the onset of such phenomena (e.g. dwarf novae, x-ray binaries) as well as objects which cannot be identified in advance (e.g. novae, supernovae, gamma-ray bursts). Modules have been developed for fast telescopes that respond to GRB alerts robotically in collaboration with the coordination of data networks. An example of deployed T60 at the TUBITAK National Observatory (Antalya, Turkey) was carried out by embedded software of the robotic telescope (Dindar et al., 2015). The telescope responds to GRB triggers transmitted from the Goddard Space Flight Center alert system thanks to this autonomy. It uses the Gamma-Ray Explosion Coordinates Network - GCN (formerly known as the BATSE Coordinates Distribution Network, BACODINE) while doing this. There are also some pipelines designed for Gaia alerts (http://gsaweb.ast.cam.ac.uk/alerts/alertsindex) similar to GRB alerts. One of these is “AlertPipe” which is responsible for real-time detection and classification of anomalies and transient astrophysical phenomena. The pipeline works within the Gaia data processing stream. Recent advances in satellite and CCD technology have allowed for a more detailed examination. Dark energy, dark matter and exoplanet research have been accelerated thanks to these developments in technology. Advances in computer technology, the enormous expansion of new storage capacities, the diversity and organization of astronomical data have led to the addition of two new fields of study to astronomy. In particular, data mining, machine learning and artificial intelligence applications have started to be used in astronomy studies. Finding solutions to the problems in astronomy with big data and subjects of big data in astronomy are discussed under the relevant subheadings below. 16 ASTRONOMICAL DATA 2. Solving Problems in Astronomy with Big Data Statistics plays an essential role in data-rich astronomy. Scientific insights cannot be extracted from massive datasets without statistical analysis. The statistical challenges are not simple; image analysis, time series analysis, nonlinear regression, survival analysis, and multivariate classification are all critically important (Feigelson and Babu, 2012). Data in a method called DFS (Distributed File System) is placed wherever there is a free computer on Earth. For example, a part of the picture you upload to Facebook can be held on a computer in China and the other part can be held on a computer in Canada. Hadoop combines these two pieces of information in milliseconds when you click to view. Astronomy was developed in two main areas namely “Astrostatistics” and “Astroinformatics”. Astrostatistics can be summarized as the application of the science of statistics to the sciences of astronomy and astrophysics. Astroinformatics can be defined as computer programs and analysis methods developed to process big data from telescopes. For example, CALTECH’s space telescope GALEX (The Galaxy Evolution Explorer) 30 TB, Australia’s SkyMapper (Southern Sky Survey) 500 Terabyte, and NASA JPL’s Hawaii telescope PanSTARRS 40 PB is generating data while the data produced by Palomar Observatory is 3 TB. The amount of data generated reaches almost zettabytes when we combine all the telescopes in the world. The International Virtual Observatory Association (http://www.ivoa.net) established for this purpose is designed to combine information from telescopes all around the world with Hadoop to establish an environment accessible to every astronomer. A virtual observatory has been set up and all data from telescopes so far has been shared, and when astronomers want to analyze a region, they can access information from telescopes on a single screen and make virtual observations. In short, the virtual observatory makes it easier for scientists to make science.
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